Television receiving apparatus



Filed March 15, 1939 mEhm zmw rozm: mm. mist INVENTOR R BERT L FREEMANkw. M n I 4 H441 8 .J 0 0 0 v 0 6 c a 52 55 65.582 5:25 65:85 65:85@5555; 102.368 992 0 Q- O & 3 m; N; 9%? 701 ATTORNEY Patented Oct. 21,-1941 Robert L. Fl

, N. Y., anignor to Freeman, aching Hueltine Corporation, a corporationof Delaware Application March 15, 1939, Serial No. 281,910

13 Claims. (Cl. 178-43) This invention relates to television receivingapparatus and is especially directed to the prqvision of an improvedsystem for detecting a television signal-carrier wave to derive itslightmodulation components, for black-level setting of such detectedcomponents, for development of separated synchronizing-signalcomponents, and for automatic amplification control in such receivingapparatus.

In accordance with present television practice, a transmitted signalcomprises a carrier wave modulated during successive intervals or traceperiods by high-frequency and unidirectional light-modulation componentsrepresentative of varying light values over successive incremental areasof an image being transmitted and of its average backgroundillumination, respectively. The carrier wave is unmodulated by lightrepresentative components during retrace periods, ordinarily having anamplitude level during portions of such periods which has a fixedrelation to black in the transmitted image, .and being modulated duringtheremaining portions of such periods by synchronizing-signal componentswhich correspond to initiations of successive lines and fields in thescanning of the image. The latter components ordinarily have amplitudevalues outside of the amplitude range of the light-modulation componentsand extend in the direction of black. I

At the receiver a generated scanning beam is so deflected as to scan andilluminate a target in a series of fields of parallel lines. Thesynchronizing-signal components of the received signal are utilized tocontrol the scanning apparatus so as to synchronize its operation withthat of similar apparatus utilized at the transmitter in developing thesignal. The intensity of the cathode ray is controlled by thelight-modulation components of the received signal, including thevideo-frequency and unidirectional background-illumination voltages,thereby to reconstruct the transmitted image.

Essential functions which must be performed in a television receivingsystem of the type described include detecting the signal-carrier waveto derive the light-modulation components; de-

riving from the detected signal separated line-frequency andfield-frequency synchronizing pulses; developing a unidirectional-biasvoltage representative of the average intensity of the carrier wave andindependent of its light-modulation components; utilizing this voltageautomatically to control one or more operating characteristics of thereceiver, for example, to efiect automatic amplification control; andstabilizing the detected signal with respect to a predetermined shadelevel, that is, establishing a fixed amplitude level thereforcorresponding to black or another predetermined shade value, in orderthat all light-modulation-components of such amplitude will berepresented by the correct shade in the reproduced scene and lightgradations from black to white represented by the various otherlight-modulation values will be properly represented in thereconstructed scene. Various methods have heretofore been devised forperforming these functions automatically but, in general,

they have involved relatively complicated and/or unstable apparatus, orhave otherwise left something to be desired.

It is an object of the presentinvention, therefore, to provide atelevision receiver for use in a system of the type described comprisingimproved means for deriving from a received television signalcarrlerwave, the video-frequency modulation components stabilized with respectto an amplitude level thereof, corresponding to a predetermined shadevalue, for deriving the synchronizing-signal components separate fromthe other modulation components, and for deriving a unidirectionalcontrol-bias voltage representative of the average intensity of thereceived signal-carrier wave and independent of its lightmodulationcomponents.

In accordance with a feature of the present invention, there is provideda. television receiver adapted for receiving and reproducing atelevision signal-carrier wave having combined light-modulationcomponents and synchronizing-signal components, the latter havingamplitude values outside the amplitude range of the light-modulationcomponents. A single rectifying circuit is provided for deriving fromthe received signal-carrier wave an output signal including. thesynchronizing-signal components separate from the other modulationcomponents and a control efiect, suchas a unidirectional-bias voltage,proportional to the average intensity of the received signal-carrierwave and independent of its lightmodulation components. The receiveralso comprises signal-detecting means operating jointly upon the outputof the rectifying circuit and the signal-carrier wave to derive thelight-modulation components separate from the synchronizing-signalcomponents. Signal-reproducing means are provided for utilizing thedetected lighfimodulation components without the synchronizing.components. Means are further provided for utilizing the derivedsynchronizing-signal components ing device ll, which may be acathode-ray signal-reproducing tube. A line-frequency generator II and afield-irequency generator I! are also coupled to the system I! and tothe scanning elements of the image-reproducing device II in aconventional manner. The stages or units Il-ll, inclusive, excepting thesystem ii which is constructed in accordance with the present inventionand will presently be described in detail, may all be of conventionalwell-known construction so that detailed illustrations and descriptionsthereof are unnecessary herein.

for deriving from the signal the synchronizing components separate fromthe other modulation components and a diode detector, having a loadcircuit effectively connected in circuit withthe load circuit of therectifying means and operating jointly upon the output of the rectifyingmeans and the signal-carrier wave, for deriving from the signal-carrierwave light-modulation components separate from 'the synchronizingcomponents. The receiver also includes signalreproducing means forutilizing only the detected modulation components without thesynchronizing components to reproduce the translated picture. 1

Also in accordance with a feature of the invention, a televisionreceiver adapted to receive and reproduce a television signal-carrierwave modulated by combined light-modulation components andsynchronizing-signal components having amplitude values outside theamplitude range of the light-modulation components comprises, arectifier circuit including a diode rectifier for deriving from thesignal-carrier wave synchronizing-signal components separate from theother modulation components and a diode signal-detecting means connectedin circuit with the rectifying circuit and operating jointly upon theoutput of the rectifier and the signal-carrier wave to derive from thesignal-carrier wave light-modulation components separate from thesynchronizing components. The receiver also includes signal-reproducingmeans including an input circuit for utilizing only the derivedlightmodulation components to reproduce the translated picture, and theabove-mentioned diodes comprise separate load circuits series-connectedin the input circuit of the reproducing means.

For a better understanding of the invention, together with other andfurther objects thereof, reference is had to the following descriptiontaken in connection with the accompanying drawing and its scope will bepointed out in the appended claims.

In the accompanying drawing, Fig. l is a circuit diagram, partiallyschematic, of a television receiver including circuits embodying thepresent invention; Fig. 2 is a group of curves representing certainoperating characteristicsof the system of Fig. 1 to aid in theunderstanding of the invention; and Fig. 3 is a curve representing theresultant light-modulation signal developed by the system of Fig. l.

Referring now more particularly to the drawing, the system thereillustrated comprises a receiver of the superheterodyne type includingan antenna system I0, ll. connected to a radio-frequency amplifier 12,to which is connected, in

, cascade in the order named, an oscillator-modulator l3, anintermediate-frequency amplifier I4, a signal-detecting and controlvoltage-developing system l5, a video-frequency amplifier l6 including astabilizing circuit and an image-reproduc- Referring briefly, however,to the general operation of the above-described system as a whole,

television signals intercepted by the antenna circuit l0, -ll areselected and amplified in the radio-frequency amplifier I2 and suppliedto the oscillator-modulator I! wherein they are converted tointermediate-frequency signals which, in turn, are selectivelyamplified-in the intermediate-frequency amplifier l4 and delivered tothe system It. The video-frequency modulation components of thesignal-carrier wave are derived by the system It and are supplied to thevideo-frequency amplifier l6 wherein they are amplified and stabilizedand from which they are supplied in the usual manner to abrilliancy-control element of the image-reproducing device I1.

The intensity of the scanning beam of the device I1 is thus modulated orcontrolled in accordance with the light-modulation voltages impressedupon the control element of the device I! in the usual manner. Saw-toothvoltage or current waves generated in the line-frequency andfield-frequency generators l8 and I9, respectively, which are controlledby synchronizingvoltage pulses supplied from the system 15, as presentlyto be explained, are applied to the scanning elements of the device H toproduce electric scanning fields, thereby to deflect the beam intwodirections normal to each other so as to trace a rectilinear scanningpattern on the screen of the reproducing device and thereby toreconstruct the transmitted image.

Referring now more particularly to the system i5 of the receiver, whichembodies the present invention, the output circuit of theintermediate-frequency amplifier l4 includes the primary winding 20 of atransformer 2| having secondary windings 22 and 22a which are preferablytuned to the intermediate-carrier frequency by condensers 23 and 23a.The winding 22 is coupled to a diode rectifier 24. This rectifier isprovided with a load circuit comprising a parallelconnected resistor 25and condenser 26 having a large time constant, preferably considerablygreater than the period of the line-synchronizing pulses, for derivingan automatic amplification control bias. For conventional systemsutilizing, for example, 30 frames (60 fields) per second of 441 lines,the resistor25 may be of the order of 2,000,000 ohms and the condenser26 of the order of 0.02 microfarad providing a time constant of 0.04second. a

For the purpose of deriving the synchronizing components separate fromthe other modulation components, a short time-constant circuitcomprising a resistor 21 and capacitance 34 is included in series withthe load'circuit 26, 26 of the diode 24 and adjacent its cathode. Thecapacitance 34 may comprise, in whole or in part, the inherentcapacitance of the cathode circuit and is indicated by dotted lines.Thus, the load circuit of the rectifier 24 comprises, in effect, two

resistance-capacitance time-constant load circuits 25, 26 and 21, 3| inseries, having large small time constants, respectively.

The input circuits of the line-frequency and field-frequency generatorsl3 and I! are connected across the resistor 21 by way of. a suitablelead 28. Conventional circuits may be included in the generators l8 andIQ for separating the line-synchronizing and field-synchronizing pulsesfrom each other. In order automatically to maintain the amplitude of thesignal-carrier wave, independent of light-modulation components, at theinput of the signal detector within a relatively narrow range for a widerange of received signals, the negative terminal of resistor 25 isconnected, by way of a suitable filter including a series resistor 23and shunt condensers 36 and by way of A. V. C. conductor 3|, to thecontrol electrodes of one or more of the vacuum tubes included in theamplifier i2, oscillator-modulator i3, and amplifier id, as shown.

For the purpose of deriving the video-frequency.

modulation-signal components stabilized with respect to the amplitudelevel thereof representing black, there is provided a diode rectifier32, connected across the secondary circuit 22a, 23a ofintermediate-frequency transformer 2i, so that the diodes 24 and 32 areeflectively connected in parallel for application of the carrier wavethereto and so that diode rectifier 32 is efiective to operate jointlyon the signal-carrier wave and the output of the rectifying circuitincluding diode rectifier 2d. The rectifier 32 is provided with a loadcircuit comprising a series-connected resistor 35 and inductance 36providing a suitable uniform impedance across the video-Irequency bandfor developing the modulation signal.

The operation of the system in accordance with the present invention maybest be explained with reference to the curves of Fig. 2, in which curveA illustrates the load characteristics of the rectifier 24 with respectto the short time-constant load circuit 21, 33 for a givensignal-carrier and wave amplitude, the abscissae representing apthe waveform of the envelope of the negativelymodulated carrier-wave signaldeveloped in the output circuit of the intermediate-frequency amplifieri4 and applied by way of the trans-.

former 2! to the diode 24, For the purpose of simplicity, only a fewline-frequency cycles are shown. The light-modulation or video-frequencycomponents and synchronizing-signal components are indicated at V and S,respectively, the latter, it will be noted, extending beyond theamplitude range of the former. Signal levels corresponding to white andblack are indicated in the figure at W and B, respectively.

It will be seen that the rectifier 24 operates as a peak rectifier andpasses current only during the occurrence of synchronizing pulses whichrepresent the peak values oi. the modulated-carrier wave, such operationbeing determined by the large time-constant load circuit comprisingresistor 25 and condenser 26. More particularly, the time constant ofthe circuit 23, 23 is such that the condenser 26 charges up toapproximately 80 per cent. of the peak value of the applied signal,corresponding to the black level.B of the modulated signal-carrier wave,so that the load current of diode Ilfiows during the entire duration ofthe synchronizing pulses. Substantially all of the remaining amplitude01 the applied signal, which corresponds to the synchronizing pulses, isdeveloped across the short time constant circuit 21, 34, the diode 24,with the time-constant circuit 21, 34, thus acting also as asynchronizing-signal detector.

Thus, the voltage built up across the load circuit 25, 26 is essentiallya unidirectional negativebias voltage, illustrated by curve e in Fig. 2,the average value of which is proportional to the peak' amplitude of thesignal-carrier wave, in the given case per cent. of the peak amplitude,and independent of its light-modulation components. The filtercomprising the resistor 29 and condensers 33 serves to remove residualfluctuations from the rectified voltage and the resultant steadyunidirectional-bias voltage is impressed negatively on'the control gridsof one or more of the tubes in the stages i2, i3, and id to control theamplification of these stages in verselyin accordance with the maximumvalue time-constant circuit 25, 23, also acts efiectively as a delaybias on the diode 2d acting with the short time-constant load circuit21, at, as a synchronizing-signal detector, since the diode 23 passescurrent only during the occurrence of the synchronizing pulses,representing the charging current of condenser 26. Hence, the detectedsynchronizing-signal voltage pulses appear across the shorttime-constant load circuit2l, 33 free from the light-modulationcomponents of the signal, as illustrated by curve 2' of Fig. 2. Thesepulses are applied by way of the lead 28 to the generators I8 and I9, inwhich conventional separating apparatus serves to separate thelinesynchronizing and field-synchronizing pulses from each other andthese pulses are utilized to maintain the generators I 3 and IS insynchronism with the corresponding apparatus at the transmitter, in theusual manner.

The intermediate-frequency voltages are also applied to the diode 32 byway of the secondary circuit 221:, 23a and this diode operates as aconventional diode signal detector, developing across its load circuit35, 36 the complete modulation signal having a waveform corresponding tohalf the modulation envelope illustrated by curve C oi Fig. 2. Thesynchronizing voltagev pulses 'developed across the load circuit 21, 34,however, represent an inversion of the synchronizing pulses of thesignal detected by the diode 32. Hence, by properly proportioning theimpedances 01' load circuits 21, 34 and 35, 36, the modulationcomponents, developed by the diode 32, and the separated synchronizingcomponents, developed by-the diode 24, are diflerentially combined sothat the total voltage across these load circuits, which'are eflectivelyin series in the input circuit of video-frequency amplifier l6,comprises the video-frequency signal without the synchronizing pulses,as illustrated by the curve M of Fig. 3 in which these suppressedsynchronizing pulses are indicated by dotted lines. This signal thus hasan amplitude level corresponding to black throughout, indicated at B inFig. 3, whereby it may be readily stabilized with respect to this level.Since this signal is poled with black most negative, it may be applieddirectly to the cathode-ray tube control grid or by way of the amplifierl6. For correct polarity, with the .arrangement shown, an even' numberof videofiled July 27, 1938. It will thus be seen that the system 15suppresses or removes the'synchronizing pulses from the signal so thatthe stabilizing means in the amplifier [6 may maintain a fixed blacklevel .for the signal at the input circuit of the signal-reproducingdevice regardless of the signal amplitude or other operating conditions.

The single rectifiying-detective system l thus includes thesignal-detecting means 32 effective to derive from the receivedtelevision signalcarrier wave the video-frequency modulation signalwithout the synchronizing components and stabilized with respect to theblack level thereof, while the single rectifying circuit thereofcomprising diode 24 is eifective to derive a unidirectional-bias voltageproportional to the intensity of the modulated signal carrier andindependent of its light-modulation components for use as an automaticcontrol voltage, and the synchronizing-modulation components separatefrom the other modulation components.

While there has been described what is at present considered to be thepreferred embodiment of this invention, it will be obvious to thoseskilled in the art that various changes and modi fications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:

1. A-television receiver adapted to receive and reproduce a televisionsignal-carrier wave modulated by combined light-modulation componentsand synchronizing-signal components having amplitude values outside theamplitude range of the light-modulation components comprising, a singlerectifying circuit for deriving from said signal-carrier wave an outputsignal including said synchronizing-signal components separate from saidother modulation components and a control effect proportional to theaverage amplitude of said carrier wave and independent oflight-modulation components,. signal-detecting means operating jointlyupon said output of said rectifying circuit and said signal-carrier waveto derive said light-modulation components separate from saidsynchronizing-signal components, means for utilizing said control effectfor controlling an operating, characteristic of the receiver, means forutilizing said separated synchronizing components 'for synchronizing theoperation of the receiver, and signal-reproducing means for utilizingsaid derived light-modulation components.

2. A television receiver adapted to receive and reproduce a televisionsignal-carrier wave modulated by combined light-modulation componentsseparate from said other modulation components and a control effectproportional to the average amplitude of said carrier wave andindependent of light-modulation components, signal-detecting means forderiving from said signal said modulation components, means forutilizing said separated synchronizing-signal components for suppressingthe synchronizing components from said detected modulation components,signalreproducing means for utilizing said detected light-modulationcomponents without said synchronizing components, means for utilizingsaid control effect for controlling an operating characteristic of thereceiver, and means for utilizing said separated synchronizingcomponents for synchronizing the operation of the receiver.

3. A television receiver adapted to receive and reproduce a televisionsignal-carrier wave modulated by combined light-modulation componentsand synchronizing-signal components having amplitude values outside theamplitude range of the light-modulation components, said wave having awide range of signal-input intensities, comprising a single rectifyingcircuit for deriving from said signal-carrier wave a controlbias voltageproportional to the average amplitude of said carrier wave andindependent of light-modulation components and for deriving from saidsignal-carrier wave said synchronizing-signal components separate fromthe other modulation components, signal-detecting means for derivingfrom said signal-carrier wave said modulation components, means forutilizing said separated synchronizing components for suppressing thesynchronizing components from said detected modulation components,signal-reproducing means for utilizing said detected lightmodulationcomponents without said synchronizing components, means for utilizingsaid controlbias voltage for maintaining the amplitude of the signaloutput of said receiver within a relatively narrow range for a widerange of received signal-input intensities, and means for utilizing saidsynchronizing components to synchronize the operation of the receiver.

4. A television receiver adapted to receive and reproduce a televisionsignal-carrier wave modulated by combined light-modulation componentsand synchronizing-signal components having amplitude values outside theamplitude range of the light-modulation components comprising, a singlepeak-rectifying circuit for deriving from said signal a control-biasvoltage proportional to'the peak value of said carrier wave and fordeveloping from said signal said synchronizing components separate fromthe other modulation components, signal-detecting means for derivingfrom said. signal the modulation components, means for combining saidseparated synchronizing components and said detected modulationcomponents with such polarity as to suppress the synchronizingcomponents from said detected modulation components, signal-reproducingmeans for utilizing said detected modulation components without saidsynchronizing components, means for utilizing said control-bias voltagefor controlling an operating characteristic of said receiver, and meansfor utilizing said separated synchronizing components for synchronizingthe operation of the receiver.

5. A television receiver adapted to receive and reproduce a televisionsignal-carrier wave modulated by combined light-modulation andsynchronizing-signal components having amplitude values outside theamplitude range of the light-modulation components comprising, a dioderectifier for deriving from said carrierwave a control-bias voltageproportional to the average amplitude of said wave and independent ofits light-modulation components, impedance means in circuit with saidrectifier for deriving from aauaaao said wave saidsynchronizing-signalcomponents separate from the other modulationcomponents, a diode detector for deriving from said signal saidmodulation components, means for diil'erentially combining saidseparated synchronizing, components and said detected modulationcomponents to suppress the synchronizing com. ponents from the detectedmodulation components, signal-reproducing means for utilizing saiddetected modulation components without said synchronizing components,means for utilizing said control-bias voltage for controlling anoperating characteristic of the receiver, and means for utilizing saidseparated synchronizing components for synchronizing the operation ofthe receiver.

6. A television receiver adapted to receive and reproduce a televisionsignal-carrier wave modulated by combined light-modulation andsynchronizing-signal components having amplitude values outside theamplitude range of the lightmodulation components comprising, a dioderectifier having a load circuit including a long timeconstant circuitfor deriving from said signalcarrier wave a control-bias voltageproportional to the intensity of the carrier wave and independent of itslight-modulation components and a short time-constant circuit forderiving from said wave synchronizing-signal components separate fromthe other modulation components, means for detecting said signal toderive its modulation components, means for utilizing said control-biasvoltage for controlling an operating of the light-modulation componentscomprising,

a diode rectifier for deriving from said carrier wave a control eifectproportional to the average amplitude of said carrier wave andindependent of light-modulation components and having a load impedancefor deriving from said wave said synchronizing-signal components, adiode detector having a load circuit effectively connected in serieswith said load impedance of said rectifying means for deriving from saidcarrier wave said light-modulation components separate from saidsynchronizing components, means for utilizing said control effect forcontrolling an operating characteristic of the receiver, means forutilizing said separated synchronizing components for synchronizing theoperation of the receiver, and signal-reproducing means for utilizingsaid light-modulation components without said synchronizing components.A

8. A television receiver adapted to receive and reproduce a televisionsignal-carrier wave modulated by combined light-modulation componentsand synchronizing-signal components having amplitude values outside theamplitude range of the light-modulation components comprising, detectingmeans for deriving from said signal said modulation components, arectifying circuit for deriving from said signal saidsynchronizing-signal components separate from said other modulationcomponents, means for difl'erentially combining said separatedsynchronizing components and said detected modulation components tosuppress said synchronizing components from said detected modulationcomponents, and sig- 9. A television receiver adapted to receive andreproduce a television signal-carrier wave modulated by combinedlight-modulation and synchronizing-signal components having amplitudevalues outside the amplitude range of the lightmodulation componentscomprising, a pair of diodes effectively connected in parallelfor theapplication of said carrier wave thereto, one of said diodes having along time-constant load circuit for developing from said carrier wave acontrol-bias voltage proportional to the average amplitude of said waveand independent of its lightmodulation components and a shorttime-consta'nt circuit for deriving from said wave saidsynchronizing-signal components separate from the other modulationcomponents, said other diode having a load circuit eifectively connectedin series with said short time-constant circuit with such polarity as toderive from said carrier wave said modulation components with saidsynchronizing components suppressed, signal-reproducing means forutilizing said detected modulation components without said synchronizingcomponents, means for utilizing said control-bias voltage forcontrolling an operating characteristic of the receiver, and means forutilizing said separated synchronizing components for synchronizing theoperation of the receiver.

10. A television receiver adapted to receive and reproduce a televisionsignal-carrier wave modulated by combined light-modulation componentsand synchronizing-signal components having amplitude values outside theamplitude range of the light-modulation components comprising, meansincluding rectifying means having a load circuit for deriving from saidsignal said synchronizing components separate from said other modulationcomponents, a diode detector having a load circuit effectively connectedin circuit with said load circuit of said rectifying means and operatingjointly upon the output of said rectifying means and said signal-carrierwave to derive from said signal-carrier wave light-modulation componentsseparate from said synchronizing components, and signal-reproducingmeans for utilizing only said detected modulation components withoutsaid synchronizing components to reproduce the translated picture.

11. A television receiver adapted to receive and reproduce a televisionsignal-carrier wave modulated by combined light-modulation componentsand synchronizing-signal components having amplitude values outside theamplitude range of the light-modulation components comprising, meansincluding rectifying means having a load impedance for deriving fromsaid signal said synchronizing components separate from said othermodulation components, a diode detector having a load circuiteffectively connected in series with said load impedance of saidrectifying means to derive from said signal-carrier wavelight-modulation components separate from said synchronizing components,and signal-reproducing means for utilizing only said detected modulationcomponents without said synchronizing components to reproduce thetranslated picture.

12. A television receiver adapted to receive and reproduce a televisionsignal-carrier wave modulated by combined light-modulation andsynchronizing-signal components having amplitude values outside theamplitude range of the lightmodulation components comprising, a pair ofdi-. odes efiectively connected in parallel for the application of saidcarrier wave thereto, one of said diodes having a load impedance circuitfor deriving from said wave said synchronizing-signal componentsseparate from the other modulation components, said other diode having aload circuit effectively connected in series with said load-impedancecircuit with such polarity as to derive from said carrier wave saidmodulation components with said synchronizing components suppressed, andsignal-reproducing means for utilizing only said last-mentionedmodulation components to reproduce the translated picture.

13. A television receiver adapted to receive and reproduce a televisionsignal-carrier wave modulated by combined light-modulation components.20

and synchronizing-signal components having amplitude values outside theamplitude range of the light-modulation components comprising, arectifier circuit including a diode rectifier for deriving from saidsignal-carrier wave said synchronizing-signal components separate fromsaid other modulation components, diode signal-detecting means connectedin circuit with said rectifying circuit and operating jointly upon theoutput of said rectifier and said signal-carrier wave to derive fromsaid signal-carrier wave said light-modulation components separate fromsaid synchronizing components, and signal-reproducing means including aninput circuit for utilizing only said derived light-modulationcomponents to reproduce the translated picture, said diodes comprisingseparate load circuits series-connected in the input circuit of saidsignal-reproducing means.

ROBERT L. FREEMAN.

